Generally, an iron core of a large-capacity transformer has a structure formed by stacking thin-sheet type magnetic bodies (for example, electromagnetic steel sheets, amorphous sheets, or the like). For example, PTL 1 (Japanese Utility Model Laying-Open No. 60-81618) discloses composing an iron core by bending a band-like ferromagnetic sheet, in order to facilitate an operation of assembling the iron core. At a bent portion of the ferromagnetic sheet, a punched hole or a cutout hole is formed with small connecting portions being left in a width direction.
On the other hand, in order to improve efficiency of a transformer, it is required to reduce loss in the transformer. The loss in the transformer includes eddy current loss due to leaked magnetic flux from a coil. Techniques for reducing eddy current loss have been proposed in the past.
For example, PTL 2 (Japanese Patent Laying-Open No. 2003-347134) and PTL 3 (Japanese Patent Laying-Open No. 1-259514) each disclose a structure of an iron core for reducing eddy current loss. Specifically, PTL 2 discloses forming slits in a horizontal direction in both of upper and lower ring yokes sandwiching a stacked block iron core. PTL 3 discloses forming slits in yokes provided at both ends of a main iron core with gaps, along magnetic flux density distribution.
Further, for example, PTL 4 to PTL 6 (Japanese Utility Model Laying-Open No. 60-57115, Japanese Patent Laying-Open No. 10-116741, and Japanese Patent Laying-Open No. 2001-35733) each disclose a structure of an electromagnetic shield attached to an inner wall surface of a tank for accommodating a transformer. For example, PTL 4 (Japanese Utility Model Laying-Open No. 60-57115) discloses a shield sheet having a plurality of slits or grooves formed therein. The slits or grooves are formed on both upper and lower end sides of the shield sheet serving as an inflow portion and an outflow portion for magnetic flux to have a depth deeper than a permeation depth of the magnetic flux, and extend along a width direction of the shield sheet.
For example, PTL 5 (Japanese Patent Laying-Open No. 10-116741) discloses an electromagnetic shield formed by stacking silicon steel strips. At least one slit is formed in a surface of the silicon steel strips, along a longitudinal direction thereof. For example, PTL 6 (Japanese Patent Laying-Open No. 2001-35733) discloses an electromagnetic shield formed by stacking magnetic bodies inside a tank. For example, a slit is provided only on a surface side of the electromagnetic shield.
PTL 7 (Japanese Utility Model Laying-Open No. 62-32518) discloses an electromagnetic shield member formed to cover upper, lower, and side surfaces of windings. A plurality of slits are formed in the electromagnetic shield member. PTL 8 (Japanese Patent Laying-Open No. 2003-203813) discloses forming a slit in a magnetic conductor provided at least one of upper and lower surfaces of a planar conductor coil.